Class loading of a Java Virtual Machine (JVM) is usually slow and consumes large amounts of memory. When a second JVM is started, only parts of the classes are being reused. If classes or libraries are being shared between JVM's, the class or library is given to other JVM's via a reference to this a first JVM's memory address space. This can be slow and result in synchronization costs on large access rates specifically in massive distributed environments and supercomputers.